311 4.4. Advances and Perspectives in PECDs 311 4.4.1. Use of Ionic Liquids in PECDs 311 4.4.2. EC Blends, Laminates, and Composites 311 4.4.3. EC Nanotubes 312 4.4.4. EC Nanofibers 312 4.4.5. Strictly All-Polymer ECDs 312 4.4.6. Advances and Perspectives in e-Paper Devices 312 4.4.7. First Inkjet-Printed ECD 313 4.4.8. Photoelectrochromic Devices (PhotoECDs) 313 4.4.9. Light-Pen Input Device 313 5. Conclusions and Outlook 314 6. Glossary 314 7. Acknowledgments 315 8. References 315

Organic electronics are broadly anticipated to impact the development of flexible thin-film device technologies. Among these, solution-processable π-conjugated polymers and small molecules are proving particularly promising in field-effect transistors and bulk heterojunction solar cells. This Perspective analyzes some of the most exciting strategies recently suggested in the design and structural organization of π-functional materials for transistor and solar cell applications. Emphasis is placed on the interplay between molecular structure, self-assembling properties, nanoscale and mesoscale ordering, and device efficiency parameters. A critical look at the various approaches used to optimize both materials and device performance is provided to assist in the identification of new directions and further advances.

The correlation between the nature of alkyl substituents on N-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD)-based polymers and solar cell device performance has been investigated. After adjusting device parameters, these TPD-based polymers used with PC(61)BM provided photovoltaic responses ranging from 4.0% to 6.8%, depending on the size and shape of the alkyl solubilizing groups. Further, we have correlated the effect of the alkyl groups on the structural order and orientation of the polymer backbone using grazing incidence X-ray scattering analysis, and we have demonstrated how fine-tuning of these parameters can improve the power conversion efficiency.